The lithium-ion battery cell is the premiere high-energy rechargeable energy storage technology of the present day. Unfortunately, its high performance still falls short of energy density goals in applications ranging from telecommunications to biomedical. Although a number of factors within the cell contribute to this performance parameter, the most crucial ones relate to how much energy can be stored in the electrode materials of the cell.
During the course of development of rechargeable electrochemical cells, such as lithium (Li) and lithium-ion battery cells and the like, numerous materials capable of reversibly accommodating lithium ions have been investigated. Among these, occlusion and intercalation materials, such a carbonaceous compounds, layered transition metal oxide and three dimensional pathway spinels have proved to be particularly well-suited to such applications. However, even while performing reasonably well in recycling electrical storage systems of significant capacity, many of these materials exhibit detrimental properties, such as marginal environmental compatibility and safety, which detract from the ultimate acceptability of the rechargeable cells. In addition, some of the more promising materials are available only at costs that limit widespread use. However, of most importance is the fact that the present state of the art materials have the capability to store relatively low capacity of charge per weight of material (specific capacity, mAh/g) or energy per weight (specific energy, Wh/kg).
Materials of choice in the fabrication of rechargeable battery cells, particularly highly desirable and broadly implemented Li-ion cells, have for some considerable time centered upon graphitic negative electrode compositions, which provide respectable capacity levels in the range of 300 mAh/g. Complementary positive electrode materials in present cells use less effective layered intercalation compounds, such as LiCoO2, which generally provides capacities in the range of 150 mAh/g. Alternative intercalation materials, such as LiNiO2, and LiMn2O4, have more recently gained favor in the industry, since, although exhibiting no appreciable increase in specific capacity, these compounds are available at lower cost and provide a greater margin of environmental acceptability.
Due to increasing demand for ever more compact electrical energy storage and delivery systems for all manner of advancing technologies, the search continues for battery cell materials capable of, on the one hand, providing greater specific capacity over wider ranges of cycling rates, voltages, and operating temperatures, while, on the other hand, presenting fewer environmental hazards and greater availability at lower processing and fabrication costs. Searches for more effective positive electrode materials, in particular, have become far-reaching with attention turning more frequently to the abundant lower toxicity transition metal compounds, which are typically accessible at economical costs.
In the intense search of material systems which can deliver much higher specific capacities and energy, interest has shifted to examination of the more active fluoride compounds. Recently, Badway et al. (Journal of The Electrochemical Society, 150(9) A1209-A1218 (2003)) reported the use of carbon metal fluoride nanocomposites to enable the electrochemical activity of metal fluorides. Their studies have shown that reducing the particle size of metal fluoride to the nanodimensions in combination with highly conductive carbon resulted in the enablement of a new metal fluoride conversion process positive electrodes resulting in a major improvement in specific capacity relative to current state of the art. Badway et al. reported>90% recovery of the FeF3 theoretical capacity (>600 mAh/g mAh/g) in the 4.5-1.5 V region through reversible conversion, which is a fundamentally different energy storage mechanism compared with the present state of the art intercalation.
Despite this success, the full utilization of certain metal fluorides, such as copper fluoride, has not been realized. Researchers have tried to enable this high energy density compound for more than 30 years with only limited success because of poor utilization of the material. Copper fluoride has a theoretical conversion potential of approximately 3.2 V, and a discharge specific capacity of approximately 520 mAh/g, leading to an exceptionally high energy density in excess of 1500 Wh/kg. Such capacity values are over 300% higher than those attained in present day state-of-the-art rechargeable Li battery cells based on LiCoO2 intercalation compounds. With respect to existing primary cathode compounds, copper fluoride would exceed the widely utilized MnO2 energy density by almost a factor of two.
Hence, there is a need in the art for electrical energy-storage and delivery systems that utilize copper fluoride effectively.